Alternator Basics

download Alternator Basics

of 12

Embed Size (px)

Transcript of Alternator Basics

Alternator Basic TheoryFor generating electricity/induction we require

Coil Magnet Relative motion between the two

N

S

Alternator Basic TheoryBicycle DynamoSimplest & most basic form of alternator is bicycle dynamo. Principle Rotor is a Two Pole Permanent Magnet. Voltage w Speed. Voltage w Strength of the magnet. (Can not be adjusted).

Alternator Basic TheoryBrush SystemPermanent magnet used earlier can be Principle replaced by an electromagnet. Output voltage can be adjusted at the same speed by changing DC supply. Disadvantages Two Carbon brushes are required to be used.

Alternator Basic TheoryBrushless Separate excitation SystemIn order to avoid use of brushes we have to use a small alternator named Exciter. Principle Main Field, Rotating Rectifiers & Exciter Armature are mounted on the same shaft. Excitation supply comes from battery to exciter field instead of main field. In this case the DC power required for excitation is much lesser. Disadvantages This is an open loop system & input to exciter does not vary for variation in output voltage.

Alternator Basic TheorySelf Excited & Regulated Shunt System In order to give correction in the exciter input according to the voltage output we have to use AVR. Principle Different Types of AVRs are being used in DG sets. The one that is being used currently is Basler DECS

Short Circuit Main Main Back Up CTs Field Armature

Surge Suppressor

Rotating Rectifiers

Rotor AVR Exciter Field Exciter Armature

Booster Unit

AVR

End

Alternator Basic Theory

N Main Field S

AC

Back

Alternator Separate Excitation Brush SystemMain Field Slip Rings

N

S + AC DC

-

Back

Alternator Separate Excitation Brushless SystemRotating Rectifiers Exciter N Main Field

S + AC DC -

Back

Alternator Self Excitation Brushless System RotatingN Main Field Rectifiers

Exciter

S

AC DC

Back

Phase Terminals

N

S

Neutral Terminals SCM CTS

AC DC

Back